83. Give the number of valence electrons in N, As, Br, and Se. Predict the number of covalent bonds needed for each of these elements to satisfy the octet rule.
84. Locate the sigma and pi bonds in each of the molecules shown below. a. H — C — H O — — b. H — C———C — H
85. In the molecules CO, C O 2 , and C H 2 O, which C—O bond is the shortest? Which C—O bond is the strongest?
86. Consider the carbon-nitrogen bonds shown below:
H C — N — H — H H — — H — and C N≡ -
Which bond is shorter? Which is stronger?
87. Rank each of the molecules below in order of the short- est to the longest sulfur-oxygen bond length.
a. S O 2 b. S O 3 2— c. S O 4 2—
Section 8.2
Mastering Concepts
88. Explain how molecular compounds are named.
89. When is a molecular compound named as an acid?
90. Explain the difference between sulfur hexafluoride and disulfur tetrafluoride.
91. Watches The quartz crystals used in watches are made of silicon dioxide. Explain how you use the name to determine the formula for silicon dioxide.
Mastering Problems
92. Complete Table 8.8.
Table 8.8 Acid Names
Formula Name
HCI O 2 H 3 P O 4 H 2 Se HCI O 3
93. Name each molecule.
a. N F 3 c. S O 3
b. NO d. Si F 4
94. Name each molecule.
a. Se O 2 c. N 2 F 4
b. Se O 3 d. S 4 N 4
95. Write the formula for each molecule.
a. sulfur difluoride c. carbon tetrafluoride
b. silicon tetrachloride d. sulfurous acid
96. Write the formula for each molecule.
a. silicon dioxide c. chlorine trifluoride
b. bromous acid d. hydrobromic acid
Section 8.3
Mastering Concepts
97. What must you know in order to draw the Lewis struc- ture for a molecule?
98. Doping Agent Material scientists are studying the prop- erties of polymer plastics doped with As F 5 . Explain why the compound As F 5 is an exception to the octet rule.
99. Reducing Agent Boron trihydride (B H 3 ) is used as reducing agent in organic chemistry. Explain why B H 3 often forms coordinate covalent bonds with other molecules.
100. Antimony and chlorine can form antimony trichloride or antimony pentachloride. Explain how these two ele- ments can form two different compounds.
Mastering Problems
101. Draw three resonance structures for the polyatomic ion C O 3 2-.
102. Draw the Lewis structures for these molecules, each of which has a central atom that does not obey the octet rule.
a. PC l 5 c. Cl F 5
Chapter 8 • Assessment 275 Chapter Test glencoe.com
103. Draw two resonance structures for the polyatomic ion HC O 2 — .
104. Draw the Lewis structure for a molecule of each of these compounds and ions.
a. H 2 S c. S O 2
b. B F 4 — d. SeC l 2
105. Which elements in the list below are capable of forming molecules in which one of its atoms has an expanded octet? Explain your answer.
a. B d. O
b. C e. Se
c. P
Section 8.4
Mastering Concepts
106. What is the basis of the VSEPR model?
107. What is the maximum number of hybrid orbitals a carbon atom can form?
108. What is the molecular shape of each molecule? Estimate the bond angle for each molecule, assuming that there is not a lone pair.
a. A B— b. A B A— — c. A A B A— — — d. A A B A A — — — —
109. Parent Compound PC l 5 is used as a parent compound to form many other compounds. Explain the theory of hybridization and determine the number of hybrid orbitals present in a molecule of PC l 5 .
Mastering Problems
110. Complete Table 8.9 by identifying the expected hybrid on the central atom. You might find drawing the mole- cule’s Lewis structure helpful.
Table 8.9 Structures
Formula Hybrid Orbital Lewis Structure Xe F 4
Te F 4 Kr F 2 O F 2
111. Predict the molecular shape of each molecule.
a. COS b. C F 2 C l 2
112. For each molecule listed below, predict its molecular shape and bond angle, and identify the hybrid orbitals. Drawing the Lewis structure might help you.
a. SC l 2 c. HOF
b. N H 2 Cl d. B F 3
Section 8.5
Mastering Concepts
113. Describe electronegativity trends in the periodic table.
114. Explain the difference between nonpolar molecules and polar molecules.
115. Compare the location of bonding electrons in a polar covalent bond with those in a nonpolar covalent bond. Explain your answer.
116. What is the difference between a covalent molecular solid and a covalent network solid? Do their physical properties differ? Explain your answer.
Mastering Problems
117. For each pair, indicate the more polar bond by circling the negative end of its dipole.
a. C—S, C—O
b. C—F, C—N
c. P—H, P—Cl
118. For each of the bonds listed, tell which atom is more negatively charged.
a. C—H c. C—S
b. C—N d. C—O
119. Predict which bond is the most polar.
a. C—O c. C—Cl
b. Si—O d. C—Br
120. Rank the bonds according to increasing polarity.
a. C—H d. O—H
b. N—H e. Cl—H
c. Si—H
121. Refrigerant The refrigerant known as freon-14 is an ozone-damaging compound with the formula C F 4 . Why is the C F 4 molecule nonpolar even though it contains polar bonds?
122. Determine if these molecules and ion are polar. Explain your answers.
a. H 3 O + c. H 2 S
b. PC l 5 d. C F 4
123. Use Lewis structures to predict the molecular polarities for sulfur difluoride, sulfur tetrafluoride, and sulfur hexafluoride.
276 Chapter 8 • Covalent Bonding Chapter Test glencoe.com